The present invention relates to an arrangement for determining contrasting objects in a picture, the arrangement comprising an input for receiving video signal samples each of which represents the luminance of a picture element and whose order of appearance is given by a horizontal scan in combination with a vertical scan, a first output for supplying background values relating to each picture element, a second output for supplying the indication that the picture element belongs to a contrasting object, at least a processing block provided with members for mean value calculation for calculating for each picture element different mean values of the background values, a contrast measuring member for producing a deviation value between the mean values and the luminance of the picture element, a comparator member for producing said indication by comparing the different deviation values to at least a predetermined threshold value and a background value assigning member for assigning a background value for each picture element on the basis of said mean values.
Such an arrangement is used with great advantage for, for example, recognizing preferred targets in a landscape, as is described in the article "Autothreshold-Autoscreener/ELIR System" presented at NEACON 78 and published by IEEE CH 1336-7/78/0000, pp. 1180-1185, or for recognizing shapes as described in the article by J-M. Zurcher "Extraction de contours en traitement electronique des images: II-processeur specialise pour signal video", published in the BULLETIN DE L ASSOCIATION SUISSE DES ELECTRICIENS, vol. 70, no. 11, June 1979, pp. 532-536, Zurich (CH).
In Applicant's French Patent Application FR-A 2,602,387 (U.S. Ser. No. 079,549, filed July 29, 1987) an arrangement is described now U.S. Pat. No 4,809,349, issued Feb. 28, 1989 which puts into effect a particularly efficient method for this type of application. However, the arrangement described is not suitable for processing pictures in real time.